Software engineering : Layered Architecture

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Software
Engineering

Software
 Computer software is the product that software
engineers design and build.
 It encompasses
 programs that execute within a computer of any size and
architecture
 documents that encompass hard-copy and virtual forms
 data that combine numbers and text but also includes
representations of pictorial, video, and audio information.

The evolving role of Software
 Software takes on a dual role;
 Product:- it delivers the computing potential embodied by
computer hardware or, more broadly, a network of
computers that are accessible by local hardware.
 Whether it resides within a cellular phone or operates inside a
mainframe computer, software is an information transformer—
producing, managing, acquiring, modifying, displaying, or
transmitting information that can be as simple as a single bit or
as complex as a multimedia presentation.
 Vehicle for delivering a product:-
 the basis for the control of the computer (operating systems)
 the communication of information (networks)
 the creation and control of other programs (software tools and
environments).

 The role has significant changes over a time span of little
more than 50 years
 Improvements”-
 in hardware performance
 pro-found changes in computing architectures
 vast increases in memory and storage capacity
 a wide variety of exotic input and output options
 The lone programmer of an earlier era has been replaced by
a team of software specialists, each focusing on one part of
the technology required to deliver a complex application.
 For proper estimation and management(Cost, Time, Error)

SOFTWARE
 Software is;
1. instructions (computer programs) that when executed
provide desired function and performance,
2. data structures that enable the programs to adequately
manipulate information,
3. documents that describe the operation and use of the
programs.
 Software is a logical rather than a physical system
element.

Software Characteristics
1. Software is developed or engineered, it is not
manufactured in the classical sense like hardware.
2. Software doesn't "wear out.“
Hardware Software
 software maintenance involves considerably more
complexity than hardware maintenance.

3. Although the industry is moving toward component-
based assembly, most software continues to be
custom built.
 In the hardware world, component reuse is a natural part
of the engineering process.
 Software components had a limited domain of
application.
 Modern reusable components encapsulate
 Data
 The processing applied to the data
 e.g., graphical user interfaces

The changing Nature of
Software & Software
Applications
 Key element in the evolution of computer-based
systems and products
 Evolved from a specialized problem solving and
information analysis tool to an industry in itself.
 Limiting factor in the continuing evolution of
computer-based systems.

 System software
 System software is a collection of programs written to service
other programs.
 e.g., compilers, editors, operating system components, drivers
etc.
 Real-time software
 Software that monitors/analyzes/controls real-world events as
they occur is called real time.
 Business software
 Business information processing
 e.g., payroll, accounts receivable/payable, inventory

 Engineering and scientific software
 Applications range from astronomy to volcanology, from
automotive stress analysis to space shuttle orbital dynamics, and
from molecular biology to automated manufacturing
 Embedded software
 Embedded software resides in read-only memory and is used to
control products and systems for the consumer and industrial
markets.
 e.g., digital functions in an automobile such as fuel control,
dashboard displays, and braking systems
 Personal computer software
 Web-based software
 Artificial intelligence software
 AI software makes use of nonnumerical algorithms to solve complex
problems
 e.g., Expert systems, pattern recognition (image and voice), artificial
neural networks, theorem proving, and game playing

Legacy Software
 Support core business functions
 Have long life and business criticality
 Exhibit poor quality
 Complex code, poor documentation, poor testing, poor
change management
 Reasons for Evolving the Legacy Software
 (Adaptive) Must be adapted to meet the needs of new
computing environments or more modern systems, databases,
or networks
 (Perfective) Must be enhanced to implement new business
requirements
 (Corrective) Must be changed because of errors found in the
specification, design, or implementation

Legacy System Components

 Hardware - may be obsolete mainframe hardware.
 Support software - may rely on support software from
suppliers who are no longer in business.
 Application software - may be written in obsolete
programming languages.
 Application data - often incomplete and inconsistent.
 Business processes - may be constrained by software
structure and functionality.
 Business policies and rules - may be implicit and
embedded in the system software.

Layered Model
Socio-technical system
Hardware
Support software
Application software
Business processes

 Changes to one layer may require consequent changes
to layers that are both above and below.
 Reasons;
 Introduction of new facilities, higher layers need to take
advantage of these facilities.
 Changes may slow down the system; new h/w needed to
improve the system performance.
 Changes in h/w makes it impossible to manage the
interfaces.

Software Engineering
 The application of systematic, disciplined,
quantifiable approach to the development,
operation, and maintenance of software
 Software engineering is an engineering discipline that is
concerned with all aspects of software production.
 Software engineers should adopt
Systematic and organized approach to their work
Use appropriate tools and techniques depending on the problem
to be solved
The development constraints and the resources available
 Apply Engineering Concepts to developing Software
 Challenge for Software Engineers is to produce high quality
software with finite amount of resources & within a predicted
schedule

Software Engineering – Layered
Technology
Layered Technology
A quality focus: the “bedrock”
Process model: the “framework”
Methods: technical “how to’s”
Tools: CASE preferred

A quality Focus
 Every organization is rest on its commitment to quality.
 Total quality management, Six Sigma, or similar continuous improvement
culture and it is this culture ultimately leads to development of increasingly
more effective approaches to software engineering.
 The bedrock that supports software engineering is a quality focus.
Process:
 It’s a foundation layer for software engineering.
 It’s define framework for a set of key process areas (KRA) for effectively
manage and deliver quality software in a cost effective manner
 The processes define the tasks to be performed and the order in which they
are to be performed

Methods:
 It provide the technical how-to's for building software.
 Methods encompass a broad array of tasks that include
requirements analysis, design, program construction, testing, and
support.
 There could be more than one technique to perform a task and
different techniques could be used in different situations.
Tools:
 Provide automated or semi-automated support for the process,
methods and quality control.
 When tools are integrated so that information created by one tool
can be used by another, a system for the support of software
development, called computer-aided software engineering (CASE)

Process framework
Process framework
Umbrella Activities
Framework activity 1
Framework activity n
Software Process
Framework activities
work tasks
work products
milestones & deliverables
QA checkpoints
Process Framework
Umbrella Activities
•Each framework activities is populated
by a set for software engineering
actions – a collection of related tasks.
• Each action has individual work task.

Process framework
Why process :
A process defines who is doing what, when and how to
reach a certain goal.
 To build complete software process.
 Identified a small number of framework activities that
are applicable to all software projects, regardless of
their size or complexity.
 It encompasses a set of umbrella activities that are
applicable across the entire software process.

Umbrella Activities
 Software project tracking and control
 Assessing progress against the project plan.
 Take adequate action to maintain schedule.
 Formal technical reviews
 Assessing software work products in an effort to
uncover and remove errors before goes into next
action or activity.
 Software quality assurance
 Define and conducts the activities required to
ensure software quality.
 Software configuration management
 Manages the effects of change.

 Document preparation and production
 Help to create work products such as models,
documents, logs, form and list.
 Reusability management
 Define criteria for work product reuse
 Mechanisms to achieve reusable components.
 Measurement
 Define and collects process, project, and product
measures
 Assist the team in delivering software that meets
customer’s needs.
 Risk management
 Assesses risks that may effect that outcome of project
or quality of product (i.e. software)

A generic view of process
(Activities) Communication:
 Heavy communication with customers, stakeholders, team
 Encompasses requirements gathering and related
activities
 Planning:
 Workflow that is to follow
 Describe technical task, likely risk, resources will require,
work products to be produced and a work schedule.
 Modeling:
 Help developer and customer to understand requirements
(Analysis of requirements) & Design of software
 Construction
 Code generation: either manual or automated or both
 Testing – to uncover error in the code.
 Deployment:
 Delivery to the customer for evaluation

CASE (Computer-Aided Software
Engineering)
 Software systems that are intended to
provide automated support for
software process activities.
 CASE systems are often used for
method support.
 Upper-CASE
 Tools to support the early process
activities of requirements and design;
 Lower-CASE
 Tools to support later activities such as

Capability Maturity Model Integration
(CMMI)
 The Software Engineering Institute (SEI) has developed
process meta-model to measure organization different
level of process capability and maturity.
 The CMMI defines each process area in terms of
“specific goals” and the “specific practices” required to
achieve these goals.
 Specific goals establish the characteristics that must
exist if the activities implied by a process area are to be
effective.
 Specific practices refine a goal into a set of process-
related activities

Process Maturity Levels
 Level 1: Initial.
 The software process is characterized as ad hoc and occasionally
even chaotic.
 Few processes are defined, and success depends on individual effort.
 Level 2: Repeatable.
 Basic project management processes are established to track cost,
schedule, and functionality.
 The necessary process discipline is in place to repeat earlier
successes on projects with similar applications.
 Level 3: Defined.
 The software process for both management and engineering
activities is documented, standardized, and integrated into an
organization-wide software process.
 All projects use a documented and approved version of the
organization's process for developing and supporting software.
 This level includes all characteristics defined for level 2.

 Level 4: Managed.
 Detailed measures of the software process and product
quality are collected.
 Both the software process and products are quantitatively
understood and controlled using detailed measures.
 Level 5: Optimizing.
 Continuous process improvement is enabled by quantitative
feedback from the process and from testing innovative ideas
and technologies.

Key Process Areas at Each
Levels
 Process maturity level 2
 Software configuration management
 Software quality assurance
 Software subcontract management
 Software project tracking and oversight
 Software project planning
 Requirements management
 Peer reviews
 Intergroup coordination
 Software product engineering
 Integrated software management
 Training program
 Organization process definition
 Organization process focus

 Software quality management
 Quantitative process management
 Process change management
 Technology change management
 Defect prevention

 Each of the KPAs is defined by a set of key practices
that contribute to satisfying its goals.
 The key practices are policies, procedures, and
activities that must occur before a key process area has
been fully instituted.
 The SEI defines key indicators as "those key practices
or components of key practices that offer the greatest
insight into whether the goals of a key process area
have been achieved."
 Assessment questions are designed to probe for the
existence of a key indicator.

Software engineering : Layered Architecture

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Software engineering : Layered Architecture